Electrical musical instrument



Jan. 25, '1944. s, w MCKELLIP E A 2,340,002

ELECTRICAL MUS ICAL INSTRUMENT Filed June 17, 1941 2 Sheets-Sheet l L Mg M Jan. 25, 1944.

S. W. M KELLIP ET AL ELECTRI CAL MUS ICAL INSTRUMENT Filed June 17. 1941 2 SheetsSheet 2 lzyiheir n a I I,

Patented Jan. 25, 1944 S PATENT OFFICE ELECTRICAL MUSICAL INSTRUMENT Spencer W. McKellip, Wynnewood, and John R. Ford, Nat-berth, Pa"; said Ford assignor to said McKellip' Application June 17, 1941, Serial No. 398,468

"1-- 1. 14Claims.

This invention relates to electrical musical instruments, and more, particularly to electronic musical instruments of the organ type.

The principal object of the invention is to provide a novel electronic organ of the keyed oscillator type which lends itself very readily to economic production and assembly, and which is particularly adaptable to a one-manual type of organ.

Another object of the invention is to provide a novel adaptation of an electron tube oscillator circuit in a musical instrument of this character.

A further object of the invention is to provide a novel means for deriving a plurality of tones from an oscillator which constitutes a tone frequency current source, and for combining the derived tones.

A still further object of the invention is to provide a novel means for-deriving both flute and string tones from an oscillator circuit.

,A further object-of the invention is to provide anovel method-of-obtaining-tremolo effects in an instrumentof this character.

Other objects and features of the invention will beapparent hereinafter-'1 Fig llA is a,, diagrammatic illustration of a portion o ang electronic organ embodying the features of the invention; andraw a 1 v l 5'-i8. similar-illustration of the remain- -e l stru In orderthat the complete instrument may be considered in connectionqwith the following description, the two; drawing-1 sheets should be placed, .endeto-end with;Flg. 1A at the left.

Certain features of the electronic organ illustrated inthe; drawings hereof form the subject or a sole invention of Spencer W. McKellip, and such features are-claimed in a copending application, Serial No. 396,610 filed June 4, 1941.

In the following description, we shall first describe the electronic organ in general terms, and then we shall describe in detail the various features thereof.

Referring to the drawin-gs, there is illustrated schematically a complete organ embodying the features of the invention, but for simplicity of illustration only a few of the oscillator circuits are shown, as these are representative of all such circuits employed in any instance. In the illustrated embodiment, the oscillator circuits, which constitute sourcesof tone currents, are divided into two groups designated generally at A and B. While any suitable form of oscillator may be used, we prefer to employ oscillators of the inductance coupled type for reasons which will appear later. The essential component elements of the oscillators are substantially the same and are designatedsimilarly.

Each'oscillator comprises an electron tube or space discharge device V of conventional form and an associated resonant or tank circuit LilcC. Each oscillator tube is of the type employing a screen grid, and preferably pentode type tubes are employed as illustrated. The screen grid of each tube is connected through a key K and a keying resistor R12 to a suitable potential source. Further, the screen grid of each tube is preferably biased negatively by means of a biasing source S1. Normally, the key K is open and the negative bias is effective; but when the key is closed, the positive screen potential overrides the negative bias and charges the screen to the desired voltage.

Each oscillator is tuned to a particular tone frequency, and tone frequency current is derived therefrom by means of a variable inductor or transformer T comprising coils Li and L2 as a split primary and a secondary or output winding S. Winding L1 constitutes the input coil of the oscillator and is connected to the control grid of tube V, while winding L2 is the feedback coupling coil and is connected to the anode of the tube. C1 is a blocking condenser serving to isolate the grid from the plate supply source, while B is a leak resistor. The condenser C, which-is the capacitive element of the tank circuit, is shunted 'across the serially-connected inductances L1 and La. Vernier tuning is accomplishedby varying the reluctance of the magnetic flux path of the transformer, thereby varying the mutual inductance of the coils and consequently varying the resonant frequency of the tank circuit. It will be understood that each oscillator is tuned to a particular fundamental tone frequency, and the entire instrument will comprise as many oscillators as are necessary to give the desired tone or note range. Across each of the output coils S, there is connected at potentiometer P by means of which the output voltage may be varied.

The output coils S (or potentiometers P) of group A are connected in series with each other and with a common load resistor or voltage divider R1 via conductor l Likewise, the output coils of group B are serially connected with one another and with a load resistor R3 via conductor 2. The output coils and associated potentiometers are of low impedance (about 300 ohms), while the load resistor is of relatively high impedance (about 250,000 ohms). The voltage dividers R1 and R2 constitute a fader, by means of which the relative signal strengths of the group A and group B oscillators may be varied at will. Preferably the dividers R1 and R: are arranged to constitute a dual potentiometer so that increase of R1 is accompanied by decrease of R: and vice versa. Thus, the keyboard is effectively divided into two parts, and the relative tone strengths thereof may be varied, as described more fully hereinafter. The tone frequency currents derived from both groups of oscillators as above described are combined across resistor R: and thence supplied to a mixer tube V1 A filter condenser C: and a switch 8: are serially con- 'tothlgresistorattappoints. Theresistorsin turn-are connected respectively via conductors 3 and 4 to resistors or voltage dividers R4 and R5 of a fader control similar to the fader ilk-R3. The voltages across R4 and R5 are combined across resistor Ra and-applied to a mixer tube V: via transformer T1.

The output circuits of tubes V1 and V: are connected, respectively. to volume control resistors Re and Re which in turn are connected to the grid of a mixer tube Va. A high frequency attenuator comprising condenser C: and variable resistor Rm is shunted across the input of tube V: to permit the attenuation of high frequencies in the entire instrument. The output circuit of tube V: is connected to a volume control resistor Ru which is controlled by a swell pedal on the instrument to control the volume of the entire instrument. The voltage across resistor R11 is supplied to a conventional amplifier C. A. which feeds into one or more loud speakers L. S. as illustrated.

In those oscillators G which are utilized to give a string tone as described hereinafter, it is desirable to Provide a frequency tremolo eifect, In the specific embodiment illustrated, the tremolo voltage'is derived from a suitable source or generator G and is applied to the control grids of the oscillator tubes. The tremolo voltage source may comprise a conventional oscillator having suitable provision for varying the frequencyand amplitude of the voltage. If desired, an oscillator of the general type employed in Groups A and B may be utilized as the tremolo voltage source.

In those oscillators from which a flute tone only is derived, one of which is shown in group A,

there is provided a grid resistor R1. as described so fully hereinafter.

Having described the organ generally. we shall now describe in detail the various features thereof. Referring to the oscillators, we employ an individual vacuum type oscillator of a modified Hartley type as described hereinafter for each note on the manual of the instrument. It is possible also to have a separate individual oscillator for each note on the pedal board of the organ, but we prefer to key the pedal board in a manner in which the pedal board switch is directly in parallel with its corresponding switch on a given note on the manual. This is not a new practice. as it has been done in the past for years on small pipe organs. of a pentode or tetrode type vacuum tube, a variable inductance, a tank tuning condenser, a rid blocking condenser. a screen grid keying bypass condenser. a grid leak, a screen series keying resistor, and an output potentiometer. In some 70 of the oscillators. we prefer to use in addition to the above-mentioned components a series grid resistor. Where a tetrode tube is used, it is very desirable to employ a negative bias resistor in this particular connection.-

1. Frequency or pitch.

2. Wave form or tone character 3. Amplitude or loudness &. Attack and decay conditions 5. Tremolo or vibrato Ithasbeenformdthatwiththeproperselection of the components that go to make up each individual oscillatontheabove conditions canbe controlledinamannertoinsurethattheomn will have the-proper musical characteristics.

Thetanktrmingcondensermostiyaifectsfrequency. Henccweusethisforcrudely settingthefrequencyoftheoscillatortoitsapproximate pitch on the tempered scale. 'Ihe grid-blocking condenaerhasverylittleaflccton frequency,butitdoeshavealargecifectonthe character or wave form of the also someefiectonthestrengthoforloud nesaniinadditim aneifectonthe tremolo condition atleasttosomedegree. However,in this grid-blockingtochangc oneimlividualfunctimfor examplewave form. thereareothermeansprovidedintheciruritto oil'setamchang'einthetrinnoloco'mlimetc. whichmightbeupsetbychangeinthe.

The screen or heying by-pass oondemer has effect on two conditions: thekeylngwitli respect toattackanddecay,andalsoclicksandplops,

andthetremoloconditionofthe This condensenhowevenisnotcriticalandittsnot nto change its value veryoften. How. ever, when a condenser is initlallychanged to w eifect a more favorable keying condition, it is an Each individual oscillator consists easymattertovarytheothercomponentstocompensateforanylechangeinthetremolo condition. Itisdesirabletohecpthecapadtyof thiscondenserassmallaspossiblewithconsistentresults. Thegridleakisnotcriticalexcept in the low frequency and where series resistors are used, and there it is to change values occasionally.

The serlesgrldresistor accomplishesanumber of things. Inanumberoforganswhichhave beenbuiltthisresistorwasutilisedintheflrst eighteennotesorsoprimarllytosmoothoutthe waveformofthefiutetone. Inusingthisresistorforthatpurpose,itisto taper-theresistancevalueofftowardsthehigher frequency until it practically becomes negligible in the circuit. It has been found, however, from experiment that it is possible with the use of a series resistor to produce a very effective woodwind tone practically devoid of even harmonics, which in some instances would be a very desirable tone. f

The series screen resistor accomplishes primarily a favorableattack and decay condition and. in conjunction with the by-pass condenser, will give a suitable attack and decay condition practically devoid of thumps and clicks. It might be well to mention at this point that a series screen resistor also plays a very important part in the strength of oscillation, and the output-derived from the oscillators can be governed to some degree by the value of this resistor. Of course, when the resistor is changed, it is necessary to make other minor changes in the circuit so that the oscillators will operate correctly.

Where a tetrode is used, and in some instances this may be desirable, it is very essential that a negative bias be applied to the tubewhen the key is open and there is no screen voltage applied to the tube. This is accomplished by a resistor connected directly from the keying lead to a D. C. negative bias source. Of course, this resistor has to be large enough that when a number of oscillators are connected together, there will be no cross modulation between oscillators from this point. This resistor and the negative bias applied through the resistor will tend to avoid spurious oscillations due to capacity coupling in the elements of the tube and similar conditions. It also tends to minimize leakage reactions in the switching mechanism and associated keying cables. Even where a pentode is used, if there should be leakage in the keying cables, it might be desirable to utilize this negative bias arrangement.

The variable tank inductance T may comprise a core about one-half inch square in cross section and formed of a stack of super-dynamo steellaminations each approximately .026 inch 1 in:

thickness. Preferablythe inductance comprises E-pieces and I-pieces with provision for movingthe I-pieces relative to the E-pieces by means of a suitable screw. The inductance of the transformer, and hence the frequency of the individual oscillator, can be very accurately set by the turning of this screw. Each individual oscillator can thus be controlled through an approximate range of live notes, plus or minus, and, in some instances, as high as three-fourths of an octave, plus or minus. This variable tuning means also eliminates a change in the other tuning components of the circuit for every note. In fact. it is only necessary to change the other tuning elements of the circuit about every three to five notes. The point where it is preferred to set the I-pieces with relation to the E-pieces is such that when the screw is turned to effect a change of say plus or minus four notes, the only actual change in the oscillation condition is frequency. All of the transformers from the lowest frequency (32 cycles) up to eighty notes above this point, which usually is as high as it is necessary to go in a small one-manual organ, may be physically the same with the exception of the size of the wire and the number of turns of the primary and secondary of the coils. It has been found necessary to vary the coils themselves only four times in a whole instrument.

It is possible to so adjust the components in each individual oscillator that there can be derived from the secondary of each oscillator a wave form that substantially approximates a flute tone. A very desirable reed-type of tone can also be derived from the'cathode of the oscillator, and a number of intermediate tones can be derived from the control grid, screen grid, and suppressor. In the one-manual instrument illustrated only the two tones are derived. The flute tone is derived from'the secondary of each individual oscillator and its'amplitude is controlled preferably by a low resistance potentiometer. It is very desirable that the impedance of the secondary winding be low. A

suitable turns ratio betweenprimary and secondaryis 40 to l step-down. Of course, the potentiometer across the secondary coil toregulate the flute output of the oscillator should be just low enough in impedance so that it does not effectively load down the primary of the oscillator. It is also very desirable to connect all the oscillators in series, as this method is characterized by low inherent loss in signal and lends itself very readily to impedance matching requirements, even in the case where eighty oscillators are connected in series. It will be readlily understood that if a parallel arrangement were used, the secondary coils would have to be high in impedance and'the'amount of loss with eighty coils connected in parallel would be tre-' mendous. Y H

The string or reed tone is taken directlyfrom the cathode of the oscillator, and since it is desirable that the cathode of each individual oscillator benear ground potential, each one of the outputs from the'cathodes' can be te minated on a 50- ohm resistance and the averagefof "each cathode maybe approximately jonlyflfi ."to 20 y will be", readily; l den stoodthat alow impedance parallel arrangement, of this character practically eliminates anyposfrom thispo int'and ohms 'aboveground. It

slbility of cross modulation times louder than a givenamount of 'iluievoltage, the amount of loss incurred ,byfa, parallel mixing arrangement j of the cathodes f jcan very; readily be gained by a suitable, step-up trans former which also takes care of ,proper impedanc'e matching intothe control grid of the flrst audio stage. I I

The following voltages seem to give optimum results with respect to oscillation stability, wave form, amplitude, and particularly keying conditions with respect to thumps and clicks:

B+ plate voltage"; to volts Screen keying voltage 75 to 90 volts Filament voltage as called for by tube rating It is very important that the 75 to 90 volts utilized for plate and keying conditions be well regulated, and the B supply utilized should have a low internal impedance as possible to avoid cross modulation at this point since the plates and screens of all of the oscillators .are com of this is to divide the keyboard into two sections. Another reason is that, where the comsubstantialfignal, is",

ponents of the oscillators are mounted-on a conventional steel chassis similar to a radio set, physical conditions are vmuch more favorable where two chassis with 40 oscillators on each are used rather than one long chassis with 80 oscillators thereon. I From each chassis, the high potential end of the series output terminates on one section of a dual potentiometer R1R:. The bottom sides of both sections of the dual potentiometer. or flute fader, are connected to ground. The sliders of both sections have a suitable high impedance resistor in series, the other sides of these two resistors being tied together and connected to the control grid of the first audio stage V1 of the mixer. Across the input of this stage, it is preferred to interpose a suitable bypass condenser C: and a switch S2, or a combination of a by.-pass condenser and a potentiometer, to provide a filter for attenuating higher harmonies of the flute tone. The dual potentiometer is so connected in the circuit that when one slider approaches ground the other slider approaches the high potential end f.'its resistor. This arrangement makes it possible for one-half of the organ to be either strengthened or diminished, while the other half is being varied in the opposite direction. This is very desirable on a one-manual organ.

We prefer to use two parallel string tone mixing dividers R of 50. ohms each, one for each chassis. One end of each of these resistors is grounded and the other ends are connected to a dual potentiometer Ri -R similar to the one already described.

The operation of the string fader is identical with the flute faden- Since the two operate independently, is possible toobtain different and varied effects, for example. it is possible to obtain a strong flute and weak string effect at the low end of the console, or any other combination that can be obtained. The only difference between the string mixer arrangementand the flute mixer is that a step up .transfoimer T1 is employed in the string. mixer so that the proper; voltage can'be impressed upon the grid of the first audio stage of the string mixer and also the impedances' mayibe properly matched at this point.

The outputs of the mixer stages are connectedto individual conventional volume controls Ba and Re which make it'possible to setthe volume of the flute independent of the string character. From these volume controls, the signal is mixed together through two high impedance resistors and then goes to the control grid of a, common mixing tube V3. Across the input of the common mixing tube, it is desirable to interpose a condenser and variable resistor filter combination to eifect attenuation of the higher harmonics of the entire instrument. The output of this stage is connected to a voltage divider R11 which is attached to the swell pedal of the organ for controlling the volume of the entire instrument in the conventional manner, which is usually with the right foot. This potentiometer may be so adjusted that it is possible to fade out the entire organ when the pedal is all the way back and, of course, the amount of signal that will get in through the system will depend entirely upon the setting of the two fader controls and the two main volume controls as well as the setting of the foot-operated swell pedal.

From the final mixer stage, the signal goes into a power amplifier C. A., which should not exceed 2% total harmonic distortion, and thence to the loud speaker. It is very desirable to use a speaker and baflle combination that is capable of covering the fundamental and harmonic range of the tones generated. The natural frequency of the loud speaker shouldbe definitely lower than the lowest frequency to be reproduced which, in the caseof the one-manual organ, is 32 cycles. The speaker should be capable of reproducing 8000 cycles at the-high frequency end.

It has been found, from actual experience, that it is not necessary to go any higher in frequency than 8000. In fact, in some organs that have been built where tweeters were used, the consensus of musical expert opinion has been that these extremely high frequencies tend to spoil the over-all tone qualities rather than enhance them.

In addition to the above-described apparatus, it is necessary to have a suitable switching mechanismthat operates in conjunction with the playing keys. In view of the fact that the keying mechanism is a one-wire system for each individual oscillator throughout, a conventional pipe organ type of coupler arrangement can be utilized. As the present invention is not concerned with the coupler, it has been deemed unnecessary'to illustrate or describe this known device. When a key is struck and a suitable coupler or stop is depressed, screen voltage is impressed on the oscillator and it starts functioning. The

The output of this tremolo oscillator is prefer-- ably passed through a cathode-load resistancecoupledistage and impressed on the grid leak of each tone oscillator that is to be tremoloed. Of

course, in the oscillators that are not to be tremoloed, the grid leak is returned directly to ground.

Also. in-t.the=case-where a pentode'tub'e is 'used' asan oscillator tube, the suppressor-grid is'also grounded. 'flhe grounding of the suppressor grid tends toshield the tube inside insuch a fashion each note enough so that a very desirable frequency tremolo condition can be effected. The phenomenon in connection with this condition is not quite clear but it is believed that the tremolo voltage applied to the control grid of the oscillator has the same effect as changing the grid resistance of the oscillator itself, and that the effect is one that actually takes place within the tube itself and is not an external condition, such as a change in inductance in the transformer due to a partial saturation of the iron of the transformer. Of course, means are provided in the tremolo oscillator and subsequent cathode-load stage to control the frequency and amplitude of the tremolo.

It is possible to effect a tremolo condition by impressing the tremolo voltage on the screen of the tube, but it is preferred to apply the tremolo voltage to the control grid because it requires less swing for a given amount of tremolo frequency shift.

With the various components that go to make up each individual oscillator plus the associated apparatus, it is possible to set the frequency ini-' tially for each note. adjust the wave form of the various tone colors derived from each oscillator, adjust the attack and decay condition, take care of the plop and click condition of the keying,-adiust the oscillators for optimum tremolo condition, set the amplitude of the tone colors derived from each oscillator independent of one another, etc.. so that a wide range of desirable tone conditions can be controlled. Moreover, the individual components that control these .conditions have very little effect on one another and, in any instance where there is an overlapping of functions, it is a simple matter to adjust the other components in such a way to accomplish the desired result.

In a one-manual organ, the playing condition is entirely diiferent than in a multiple manual organ. Accompaniment and solo condition naturally have to be all played from this one manual. It is a well-known fact that for a solo part, assuming for example the extreme condition where this solo is a one-note-at-a-time aiiair and the accompaniment to be effective is three or more notes, the solo has to be considerably louder than the accompaniment to stand out;

It is very desirable to carefully adjust the volume of each note in such a way to make this possible. Really the keyboard, as far as volume is concerned, is divided into three sections; one, for extreme bass which is strong; two, the middle section which is weak; and three, the upper section which is stronger than either of the other two. Now the adjustment of each individual note for loudness has to be done initially by ear, be? cause naturally'the ratio of voltage to actual signal hearddepends upon the wave form of, the tone that is being listened to. After each key is set with respect to volume, it, is very desirable that the wave form of each individual note be so adjusted that from one end of the instrument to the other is a constant change. 01 course,

the change in wave form and volume both are very gradual between any two notes. After each oscillator is accurately tuned to its place in a tempered scale, there is a slight drift in frequency one way or the other almost immediately, and over a period of time the frequency of each individual oscillator might change slightly. It has been found from actual experience, however, that. this shift in frequency is really an twenty-five violins is the fact that each one and each individual string of each one is slightly out of tune to start with and is played very slightly out of tune by the violinist. Exactly the same condition exists in the present organ and, in view of the three above-mentioned conditions, there is absolutely no question about an ensemble, or a combination of tones, being heard when the organ is played with two hands. It is possible to play five notes with each hand and in some cases six with each hand. Therefore, if each note is slightly different from its predecessor. and from one end of th instrument to the other there is a marked difference, naturally an en semble effect can be accomplished. Also, the three above-mentioned conditions also make-it possible for the solo to standout against an accompaniment conditlomand this condition is also still further enhanced by the use of the individual fader controls already mentioned.

In a particular. single manual .organ which was constructed according the invention and which had eighty notes, the oscillator components had structuralcharacteristics and values as set forth in the following tabla-which is, given as a speciiicexample. Y

Notes Transformers secondary 225 turns 01139 wire.

Nos. 1 to 36each primary 4500 turns of #39 wire,

Condenser-sums) Screen rm one Screen g g egg or .2 .08 .08 .2 .08 .08 .17 .08 .08 .15 .08 .08 .15 .1 .08 .1 .1 .08 .1 .1 .08 .1 .l .08 .1 .1 .(B .1 .i .(B .1 .1 .08 .08 .07 .00 .08 .07 .06 .08 .07 .06 .00 .05 .06 .06 .05 .06 .04 .04 .06 .04 .04 .05 .04 .04 .06 .03 .03 .06 .03 .03 .08 .03 .03 .06 .08 08 .06

Osmium-solids) Resistors Notes Transicrmsrs Tank Grid .03 .03 .02 .02 .02 .02 .02 .02 .0176 .02 on. 87to B-oach primarywmturnsoifi7wira, .0176 .02 secondary lwtumsoimwire. .0175 .02 .0176 .02 .015 .0176 .016 .0176 .015 .0176 .016 .0175 .0126 .015 .0126 .016 .0126 .016 .0125 .015 01 .0125 NolJfitoGO-eachprimaryfliiOturnsoifii'wire, .01 .0126 lecondarylmturnsoimwire. .01 .0126 01 .0125 .008 .000 .OCB .000 .02 .M .009

1 each prim m ire, $1 .Nos. 6 to 71 ary 1500 turns of w secondary 75turnsoif36wim .006 .006 d .005 .005 d .11) .004 .01 do .00! .004 .01 do .004 .004 01 d .004 .004 .01 d .004 .004 .01 d .(IM .004 .01

.004 .004 .01 do 70- iNos.72to80-eechprlmsry1100tumsoif34wire, 5004 .004 .01 do seoondaryooturnsoimwire. .000 .003 .01 do .78 .(DB .003 .01 meg do 500M 79.- .(XB .01 meg" ---do. 600M so .000 .01 meg ---do 500M In the same organ the components were further characterized as follows:

Tubes V wereSJ7 type Tubes V1 to Va'were 605 type ResistorsR-'-= 50 ohms Resistors R1 and Ra=250M Resistors R. and Rs=500 ohms Resistors Rs and Rs=OM Although a. specific embodiment of the invention has been described in detail for the purpose of disclosure. it will be understood that the invention is not limited thereto but is capable oi further embodiments. within the scope of the appended claims.

We claim:

1. In an electrical musical instrument, a source of tone irequency current including an electron tube of the high vacuum type having at least a cathode, an anode and a control grid, an anodegrid energy transfer path for said tube, means for deriving tone frequency current of one character from said path, a cathode circuit for said tube, and means for deriving tone frequency current of a diflerent character from said cathode circuit.

2. In an electrical musical instrument, a plurality oi sources of tone frequency current each including an electron tube 01 the high vacuum type having at least a cathode, an anode and a control grid, an anode-grid energy transfer path for each said tube, an output impedance for each said tube arranged to derive tone frequency current of one character from said path, a common output circuit for said tubes including said output impedances in series relation, a cathode circuit ior each said tube. and a second common output circuit ior deriving tone frequency current of a different character from saidcathode cir-' cuits.

3. In an electrical musical instrument, an electronic oscillator including an electron discharge 1 tube of the high vacuum type having at least a cathode, an anode, and a control grid, means coupling said anode to said grid, a cathode circuit for said tube, means for deriving tone frequency current from said anode-grid coupling means, means for deriving other tone frequency current from said cathode circuit, a source of tremolo voltage, and means for applying said voltage to the control grid of said tube. 4

4. In an electrical musical instrument, an electronic oscillator including an electron discharge tube of the high vacuum type having at least a cathode, an anode, a control grid and an auxiliary grid, means coupling said anode to said control grid, a cathode circuit for said tube, means for deriving tone frequency current from said anodecontrol grid coupling means, means ifor deriving other tone frequency current from said cathode circuit, manually-operable means for controlling the potential on said auxiliary grid to start and stop said oscillator, a source of tremolo voltage,

- and means for applying said voltage to the control 6. In an electrical musical instrument, a source of tone frequency current including an electron tube of the high vacuum type having at least a. cathode, an anode and a control grid, an anodegrid energy transfer path for said tube, means for deriving tone frequency current of one character from said path, a cathode circuit for said tube, means for deriving tone frequency current of a different character from said cathode circuit, and means for combining. said tone frequency currents.

7. An electronic organ, comprising a plurality of tone frequency current sources, each of said sources including an electron tube of the high vacuum type and a resonant circuit arranged to form an oscillator, keying means for controlling the operation of said oscillators, means for deriving tone frequency currents of different char acters from said oscillators, and means for combining aid currents,

8. An electronic organ, comprising aplurality of tone frequency current sources, each of said sources including an electron tube of the high vacuum type and a resonant circuit arranged to form an oscillator, keying means for controlling the operation of said oscillators, means for deriving tone frequency current of one character from the resonant circuit of each oscillator, means for deriving tone frequency current of a different character from another portion of each oscillator, and means for combining said currents.

9. An electronic organ, comprising a plurality of tone frequency current sources, each of said sources including an electron tube of the high vacuum type and a resonant circuit arranged to form an oscillator, keying means for controlling the operation of said oscillators, each of said oscillator tubes having a cathode, and a common voltage divider to which the tube cathodes are connected, whereby to derive tone frequency currents from said oscillators.

10. An electronic organ, comprising a plurality of tone frequency current sources, each of said sources including' an electron tube of the high vacuum type and a resonant circuit arranged to form an oscillator, keying means for controlling the operation of said oscillators, each of said oscillator tubes having a cathode, a common voltage divider to which the tube cathodes are connected, whereby to derive tone frequency current of one character from said oscillators, means for deriving tone frequency current of a different cathode circuit, at least one character from the resonant circuits of said oscillators, and means for combining said currents.

11. An electronic organ, comprising a plurality of tone frequency current sources, each of said sources including an electron tube of the high vacuum type and a resonant circuit arranged to form an oscillator, keying means for controlling the operation of said oscillators, each of said oscillator tubes having a control grid, a source of tremolo frequency voltage, means for applying said voltage to the control grids of at least some of said tubes, means for deriving tone frequency currents from said oscillators, and means for combining said currents.

12. An electronic organ, comprising a plurality of tone frequency current sources, each of said sources including an electron tube of the high vacuum type and a resonant circuit arranged to form an oscillator, keying means for controlling the operation of said oscillators, each of said oscillator tubes having a control grid and a oath ode, a source of tremolo frequency voltage, mem for applying said voltage to the control grids of said tubes, means connected to the tube cathodes for deriving tone frequency currents from said oscillators, and means for combining said cm rents.

13. An electronic organ, comprising a plurality of tone frequency current sources, each of said sources including an electron tube of the high vacuum type and a resonant circuit arranged to form an oscillator, keying means for controlling the operation of said oscillators, each of said oscillator tubes having a. control grid, a series resistor connected to the control grid of at least some of said tubes, means for deriving tone frequency currents from said oscillators, and means for combining said currents.

14. In an electrical musical instrument, a source of tone frequency current including an electron tube of the high vacuum type having at least a cathode, an anode and a control grid, on anode-gridenergy transfer path for said device, means for deriving tone frequency current of one character from said path, a cathode circuit for said device, and means for deriving tone frequency current of a difierent character from said of said tone frequency currents being substantially a sine wave.

SPENCER W. MCKELLIP. JOHN R. FORD. 

